Identifying capacitive and inductive loss in lumped element superconducting hybrid titanium nitride/aluminum resonators

TL;DR

This paper introduces a method to identify and quantify capacitive and inductive losses in superconducting resonators using mixed-material devices, revealing different loss mechanisms at various electric fields and temperatures.

Contribution

The study systematically distinguishes capacitive and inductive losses in superconducting resonators with mixed TiN and Al components, providing insights into loss origins and their dependence on material composition and temperature.

Findings

Loss at low electric field is two-level system in nature and linked to Al capacitance.

High electric field loss correlates with Al area and inductance, likely due to quasiparticles.

Interface loss between TiN and Al is negligible at 50 mK.

Abstract

We present a method to systematically locate and extract capacitive and inductive losses in superconducting resonators at microwave frequencies by use of mixed-material, lumped element devices. In these devices, ultra-low loss titanium nitride was progressively replaced with aluminum in the inter-digitated capacitor and meandered inductor elements. By measuring the power dependent loss at 50 mK as the Al-TiN fraction in each element is increased, we find that at low electric field, i.e. in the single photon limit, the loss is two level system in nature and is correlated with the amount of Al capacitance rather than the Al inductance. In the high electric field limit, the remaining loss is linearly related to the product of the Al area times its inductance and is likely due to quasiparticles generated by stray radiation. At elevated temperature, additional loss is correlated with the amount of Al in the inductance, with a power independent TiN-Al interface loss term that exponentially decreases as the temperature is reduced. The TiN-Al interface loss is vanishingly small at the 50 mK base temperature.